Polycrystalline diamond compact drill bits are sensitive to the hydraulic cooling and cleaning of the cutting face thereof. Drilling fluid is pumped down the drill string and is forcibly ejected through a plurality of nozzles to impact on the bottom of the hole. The high pressure hydraulic flow from the nozzles is the sole means of preventing the polycrystalline diamond cutters from overheating or balling up with formation cuttings.
In the prior art drill bits, the jets of drilling fluid emerging from the nozzles first impacts on the formation being penetrated by the bit. The impact of the jet is diverted by the bottom of the hole into a lateral flow respective to the borehole axis and more or less parallel to the formation surface. Hence, the jet splatters after leaving the high pressure bit nozzle, thereby producing strong flow in some directions and unsatisfactory flow in other directions. This disorderly impact of the jet of drilling fluid respective to the formation being penetrated represents an undesirable loss of hydraulic energy and results in inadequate cooling and cleaning of the cutters.
The useful life of a polycrystalline diamond cutter face or compact is greatly extended when it receives adequate lubrication and cooling from the drilling fluid. On the other hand, where the polycrystalline diamond cutter face receives inadequate fluid flow, the cutter face will ball up with the cuttings which pile up in front of the cutting surface and isolates the cutter surface from the drilling fluid. This action causes the rate of penetration of a polycrystalline diamond bit to be greatly decreased. If the ball-up condition is severe, the cutters will overheat and rapidly wear, and the bit will have to be replaced in short order.
Therefore, it would be desirable to prevent the clogging and inadequate cooling of the cutting face of a polycrystalline diamond cutter. This can be achieved by more precisely applying the available hydraulic fluid directly towards the cutting face of the cutters. A drill bit made in accordance with the present invention achieves this desirable goal.